40 - сорок /SOROK/
... - here the numbers start to count up by 10's "десят"
50 - пятьдесят /PYATDESYAT/
...
60 - шестьдесят /SHEST'DESYAT/
...
70 - семьдесят /SEM'DESYAT/
...
80 - восемьдесят /VOSEM'DESYAT/
...
90 - девяносто /DEVYANOSTO/
...
100 - сто /STO/
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These are the numerals, and they can be used for telling age by adding "years" to the phrase. There are two words for "years" that are used with different numbers:

I am 23.
мне двадцать три года.

My friend is 35.
моему другу тридцать пять лет.

Typically years that are multiples of 5 use the "лет" and other end numbers are followed by "года." There are a couple of other variations, but if you have specific numbers/dates you are interested in, just ask!

- i'm sorry but there are slight inaccuracies:
- the first three letters in 12 двенадцать must be emphasized in bold
- the first T in /SHESTNADSAT'/ is very rarely pronounced
- семнадцать and восемнадцать do not contain 'ь' after 'м', also the first apostrophe in /SEM'NADSAT'/ must be removed
- in /PYATDESYAT/ the apostrophe after the first T is missing
- /SEM'DESYAT/ and /VOSEM'DESYAT/ can alternatively be pronounced with M not palatalized
- /SHEST'DESYAT/ can alternatively be pronounced as /SHESDESYAT/ or even /SHEZDESYAT/

and there are three words for 'years', not two
the rule of 'multiple of 5' gives the right result in less than 50% of the cases
in fact, the pattern for telling age is as follows:
- all the numbers ending in 1 require 'год' (1, 21, 31...)
- all the numbers ending in 2, 3, 4 require 'года' (2, 22, 32, 42, 3, 23, 33, 43...)
these two rules have one exception - numbers 11, 12, 13, 14 require 'лет'
- all the other numbers use 'лет'